UN Secretary General Ban Ki-moon observes a moment of silence during a ceremony at UN headquarters in New York honouring the 101 UN workers killed in the Haiti earthquake. (Mary Altaffer/Associated Press)

An emotional Secretary General Ban Ki-moon paid tribute Tuesday in New York to the 101 United Nations workers who were killed in the Haiti earthquake, the single greatest loss for the world body in its 64-year history.

Hundreds of UN staff joined relatives of those who died at the ceremony at UN headquarters, listening as Ban pledged: "We will never forget you. We will carry on your work."

Cries from a young child in the audience who lost a loved one in the Jan. 12 quake punctuated the memorial tribute.

The ceremony began with a video of the victims' pictures interspersed with footage of the devastating earthquake that left more than 230,000 dead and more than 1 million homeless, and of Ban's visit five days later. It also depicted the solemn military farewell to Haiti mission chief Hedi Annabi and his deputy, Luiz Carlos da Costa, who died when the UN headquarters collapsed.

After a minute of silence to honour the UN victims, the names of the victims were read as their pictures flashed on a screen. The majority died when the headquarters and adjacent buildings were flattened. In what many observers said was his most emotional speech since taking the helm of the United Nations in January 2007, Ban began by bowing deeply to those in the audience and those watching the webcast at UN offices around the world.

"Dear colleagues, dear friends, above all to families of those to whom we sadly bid farewell," the secretary general said, his voice breaking. "We have suffered the greatest loss in our history."

He added that those who died came from all corners of the globe to help Haiti and included doctors and drivers, police officers and policy advisers, soldiers and lawyers.

"Gratitude fills this chamber — profound thanks that our world and our lives were touched by the grace and nobility of these 101 UN heroes," he said, standing in front of a table where 101 candles flickered.